Most conventional projectiles such as bullets or artillery shells are aerodynamically shaped to increase their speed and overall performance. Most commonly, the rear of a projectile fired from a firearm, artillery or the like is either cylindrical, as is the case with most artillery shells and larger caliber bullets, or configured as a “boattail”. The boattail is a truncated conical portion at the rear of a bullet, with where the conical portion begins tapering toward the rear of the bullet or projectile being a circumference around the bullet where air begins to separate from the bullet when it is in flight, causing a partial vacuum behind the bullet that creates drag.
The rear of a bullet or projectile may be configured having a recess for causing expansion of the rear of the bullet to engage rifling of a barrel and seal the bullet against the inner bore of a barrel to prevent loss of expanding gasses upon firing. Efforts have been made to eliminate or minimize drag created by the partial vacuum at the rear of a projectile by using expandable boat tails or cones, projectile shape, and tail covers in order to fill up the vacuum behind a bullet and smooth airflow immediately behind a bullet. Some projectiles such as Hall's U.S. Pat. No. 4,674,706 and Rastegar's U.S. Pat. No. 8,487,227 use a type of “tail cone” device to increase a projectile's performance by incorporating a boattail extension device to improve the aerodynamic properties at the back of the projectile. Both of these particular patents modify the aerodynamic properties of the projectile by the installation of an extending cone or layers of cones to form an overall increased aerodynamic shape in order to reduce drag. One problem with this type of design is not only the complexity of manufacturing such an expanding cone, but the higher probability of failure during its deployment due to a tremendous increase in the number of moving parts. In addition, the extreme rate of revolution of a bullet, which is typically well in excess of 100,000 RPM, may tear relatively fragile moving parts apart due to centrifugal force. For instance, a standard M16 service rifle (0.223×45) has a muzzle velocity of around 3100 feet per second with rifling of a 7 inch twist, meaning that a bullet from such a rifle rotates at around 318,900 RPM. Shrapnel that may be flung from a projectile rotating that fast would be devastating.
Another problem with this type of design is the change in center of gravity and center of pressure of the projectile while the projectile's cone is in the process of changing shapes (extending and ejecting parts, such as with the ejection of the pressure plate in Hall's design). Once the cone in these previously mentioned designs are extended (fully deployed position), there could actually be a loss of overall area for the explosion to push off against, especially since the lack of outer side walls of the concentric cones would not capture much of the explosive force, and may even allow some of the explosive force to move in between the expanding rings (cones), deforming the cone altogether. These types of expandable cones also use release mechanisms that can malfunction or not operate properly in such high force situations, such as with a standard bullet or artillery round.
The present invention overcomes these deficiencies with a fixed cone system allowing for a predictable/known center of gravity, a predictable/known center of pressure, ease of manufacturing with minimal parts, no moving parts, no loss of parts during flight, while maintaining a generally aerodynamic rear cone design, and providing for an overall increase in the base of the bullet for an increase area that an explosion can push off against.
Some other designs, such as Sieling's U.S. Pat. No. 3,809,339 attempt to overcome the moveable/extendable boat tail or cone by the use of what the inventor calls “stings,” these stings, while eliminating some of the drag caused by disrupted airflow at the aft of the projectile, do not assist the projectile's performance by increasing the explosion “push-off” area, as well as having no chamber walls to contain the explosive force. Additional embodiments of the current invention can incorporate changing the shape of the cone sections to attain different aerodynamic characteristics, while still increasing the “push-off” or base, overall area by the use of the cone chambers. Along with the overall increase in the area of the base of the projectile (push-off area), this area is housed within walls to hold the explosion for a longer period of time (chambers), with less “bleed-off” of the explosion over the edge of each base, as would happen with the sting designs of Sieling and the cone designs of Hall and Rastegar. The instant invention incorporates hollowed out cones to not only increase the projectile base, but also to hold the explosion in order to gain the full benefit of the explosive force. The instant invention's cone sections can also be incorporated into other projectile designs as such designs emerge.